Twist correction device for pipe conveyor

ABSTRACT

A twist correction device for a pipe conveyor having an endless transfer belt whose at least part is rounded in a pipe shape enclosing therein a material to be transferred. The device includes a plurality of correction rollers obliquely inclined relative to the transfer direction of the transfer belt and in pressure contact with the outer circumferential surface of the pipe-shaped transfer belt to apply correcting force to the belt for correcting twisting of the belt. The device further includes two roller support frames supporting the plurality of correction rollers and pivotally connected to a stationary support frame rotatably about axes perpendicular to the transfer direction of the transfer belt. The device includes an angle adjusting device provided on the stationary support frame for adjusting rotated angles of the roller support frames about the axes, thereby correcting twisting of the pipe-shaped transfer belt. The angle adjusting device is manually driven or automatically power driven.

BACKGROUND OF THE INVENTION

This invention relates to a device for correcting twist of a transferbelt rounded in a pipe shape of a pipe conveyor.

A pipe conveyor has been known, whose endless transfer belt is roundedover its major part in a pipe shape into which a powdery or granularmaterial is enclosed to be continuously transferred. FIGS. 1 to 4illustrate such a pipe conveyor by way of example.

In the known pipe conveyor shown in FIGS. 1 to 4, an endless flexibletransfer belt 1 has an elastic tendency of rounding about itslongitudinal axis into a pipe shape. As shown in FIG. 1, the flexibletransfer belt 1 extends around a front driving drum 2 and a rear drivendrum 3 and is flattened at drums 2 and 3.

A plurality of support frames 4 each in the form of a rectangular frameare arranged in the advancing direction of the transfer belt 1 withsubstantially equal intervals and connected with one another by means ofconnecting rods 5 extending in parallel with the advancing direction ofthe transfer belt 1. As shown in FIG. 2, each of the support frames 4 isdivided into two chambers, an upper chamber 4a in which the advancingrun 1a of the transfer belt 1 passes and a lower chamber 4b in which thereturning run 1b of the transfer belt 1 passes.

In each of the upper and lower chambers 4a and 4b, a plurality ofshape-holding rollers 6 are rotatably supported in a circle and spacedcircumferentially substantially equidistant one relative to the other.

The advancing run 1a of the transfer belt 1 in a flattened state isdriven around the driven drum 3 from its lower side to the upper sideand then guided by the support rollers 7 and 8 supporting the lowersurface and side surfaces of the run 1a so that the advancing run 1a isprogressively rounded into a trough or eavesgutter shape with the aid ofits elastic tendency.

Before the advancing run 1a of the transfer belt 1 has not been roundedsufficiently, a powdery or granular material 10 to be transferred ispoured onto the advancing run 1a from a hopper 9 provided above thedriven drum 3.

The advancing run 1a of the transfer belt 1 is then advanced into theupper chamber 4a of the nearmost support frame 4 to be guided by theshape-holding rollers 6. As a result, the advancing run 1a of thetransfer belt 1 is rounded into a pipe shape and side edges thereof areoverlapped with each other on the upper side thereof to enclose thematerial 10 in the pipe-shaped transfer belt 1.

The pipe-shaped advancing run 1a enclosing therein the material 10 issupported on its circumference by the shape-holding rollers 6 andadvances keeping its pipe shape together with the material 10 therein.

After leaving the forwardmost support frame 4 near the forward drivingdrum 2, the advancing run 1a passes through a belt flattening unit (notshown) during which the advancing run 1a is flattened so that thepowdery or granular material 10 is poured into a receiving box 11provided forwardly below the driving drum 2. The belt flattening unit isconstructed similar to and substantially in point symmetry of thematerial enclosing portion shown in FIG. 3.

After leaving the driving drum 2, the returning run 1b of the transferbelt 1 is rounded into a pipe shape in the same manner as describedabove and passes through the lower chambers 4b of the support frames 4to return to the driven drum 3. The transfer belt 1 is circulated aroundthe driving and driven drums 2 and 3 in this manner.

However, in the event that the distance between the driving and drivendrums 2 and 3 of the pipe conveyor is long, the pipe-shaped transferbelt 1 is frequently twisted about its longitudinal axis due to (a)wrong positions of the shape-holding rollers, (b) errors in accuracy inmanufacturing the shape-holding rollers and support portions thereforand (c) irregular wear of the shape-holding rollers.

In order to overcome this problem, a correction device has been proposedfor preventing or correcting the twisting of the pipe-shaped belt of apipe conveyor. In the proposed correction device, a shape-holding roller6 is arranged as a correction roller at a location where the transferbelt 1 rounded in the pipe shape tends to twist as shown in FIG. 4. Thecorrection roller 6 is inclined such that one end of the roller locatedon the side of the transfer belt 1 tending to twist is positionedforward of the other end in the advancing direction of the transferbelt 1. In this manner, the correction roller 6 gives the transfer belt1 twisting forces in a direction opposite to the direction in which thetransfer belt 1 tends to twist, thereby preventing the twisting of thepipe conveyor.

In this correcting device, however, the correcting roller contacts thetransfer belt 1 only at one point so that sufficient twisting forcescould not be given to the transfer belt. In order to eliminate thisdisadvantage, plural correcting rollers should be provided to increasethe contact points with the transfer belt to increase the twistingforces against the twisting tendency of the transfer belt.

However, the plural correction rollers must be individually inclinedrelative to the advancing direction of the pipe-shaped belt. Thisoperation is very troublesome and time-consuming and an apparatus forthis purpose becomes prohibitively complicated.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a twist correction devicefor a pipe conveyor, which eliminates all the disadvantages of the priorart, and which is able to tilt a plurality of correction rollerssimultaneously relative to the advancing direction of the transfer beltonly by one operation of only one angle adjusting device.

In order to accomplish the object, in a twist correction device for apipe conveyor having an endless transfer belt whose at least part isrounded in a pipe shape enclosing therein a material to be transferred,the device according to the invention comprises a plurality ofcorrection rollers obliquely inclined relative to the transfer directionof the transfer belt and in pressure contact with the outercircumferential surface of the pipe-shaped transfer belt to applycorrecting force to the belt for correcting twisting of the belt, tworoller support frames supporting the plurality of correction rollers,respectively, and pivotally connected to a stationary support framerotatably about axes perpendicular to the transfer direction of thetransfer belt, and angle adjusting means provided on the stationarysupport frame for adjusting the rotated angles of the roller supportframes about the axes, thereby correcting twisting of the pipe-shapedtransfer belt.

The angle adjusting means preferably includes driving means for forcedlyrotating the roller support frames about the axes. The driving means ispreferably an electric motor, hydraulic cylinder or pneumatic cylinder.

When the roller support frames are rotated about the axes by means ofthe angle adjusting means, the plurality of correction rollers mountedon the roller support frames pivotally supported by the support frameare simultaneously inclined relative to the advancing direction of thetransfer conveyor so that the respective correction rollers are broughtinto pressure contact with the outer circumferential surface of thetransfer conveyor under inclined states. Therefore, the correctionrollers give the transfer conveyor great twisting force caused by thepressure contact therewith, thereby preventing or correcting the twistof the transfer belt.

The invention will be more fully understood by referring to thefollowing detailed specification and claims taken in connection with theappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view illustrating a pipe conveyor of theprior art;

FIG. 2 is an enlarged sectional view taken along the line II--II in FIG.1;

FIG. 3 is an enlarged sectional view taken along the line III--III inFIG. 1;

FIG. 4 is a partial plan view illustrating a twist correction device ofthe prior art by way of example;

FIG. 5 is a cross-sectional view illustrating a principal part of thepipe conveyor having the twist correction device of the first embodimentaccording to the invention;

FIG. 6 is a side view illustrating the principal part shown in FIG. 5;

FIG. 7 is an exploded perspective view of the lower correction device ofthe first embodiment of the invention;

FIG. 8 is a cross-sectional view illustrating a principal part of thepipe conveyor having the twist correction device of the secondembodiment according to the invention;

FIG. 9 is an exploded perspective view of the principal part of the pipeconveyor shown in FIG. 8;

FIG. 10 is a cross-sectional plan view of the principal part of the pipeconveyor shown in FIG. 8;

FIG. 11 is a cross-sectional view illustrating a principal part of thepipe conveyor having the twist correction device of the third embodimentaccording to the invention;

FIG. 12 is a side view illustrating the principal part of the pipeconveyor shown in FIG. 11;

FIG. 13 is a cross-sectional view illustrating a principal part of thepipe conveyor having the twist correction device of the forth embodimentaccording to the invention;

FIG. 14 is a cross-sectional plan view illustrating a principal part ofthe pipe conveyor having the twist correction device of the fifthembodiment according to the invention;

FIG. 15 is a side view illustrating a principal part of the pipeconveyor having the twist correction device of the sixth embodimentaccording to the invention;

FIG. 16 is a side view illustrating a principal part of the pipeconveyor having the twist correction device of the seventh embodimentaccording to the invention;

FIG. 17 is a side view illustrating a principal part of the pipeconveyor having the twist correction device of the eighth embodimentaccording to the invention; and

FIG. 18 is a sectional front view illustrating the principal part shownin FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 5 to 7 illustrate the first embodiment of the invention. Likecomponents in the first embodiment are designated by the same referencenumerals as in FIGS. 1 to 4 and will not be described in further detail.

As shown in FIG. 5, a twist correction device A including an uppercorrection device A1 and a lower correction device A2 is provided in theupper chamber 4a in a support frame 4 where the advancing run 1a of atransfer belt 1 rounded in a pipe shape tends to twist.

The upper and lower correction devices A1 and A2 are in mirror symmetrywith each other with respect to a horizontal line between them and thelike components are denoted by the same reference numerals. Only thelower correction device will be explained. As shown in FIG. 7, the lowercorrection device A2 comprises a roller support frame 15 having aU-shaped frame plate 12 and a vertical plate 14 fixed to the frame plate12 and formed at its upper center edge with a semicircular opening 13.Reinforcing ribs 14a are fixed to the rear surface of the vertical plate14.

The roller support frame 15 is pivotally connected with the bottom ofits U-shaped frame plate 12 to a horizontal plate 16 at the mid portionof the support frame 4 by means of a vertical bolt and nut 17. It isfixed to the horizontal plate 16 by means of bolts and nuts 19 passingthrough the U-shaped frame plate 12 and through arcuate apertures 18which are formed in the horizontal plate 16 to have a center at the boltand nut 17.

As shown in FIGS. 5 and 6, the vertical plate 14 of the roller supportframe 15 is provided on its front surface with three support bearings 20which are spaced equal distances from each other along the arcuate edgeof the semicircular opening 13 and fixed to the vertical plate 14 bymeans of bolts and nuts 21. Three correction rollers 22 are supported onthe support bearings 20 through shafts 23, respectively, such that thecorrection rollers 22 are positioned somewhat radially inwardly of thearcuate edge of the semicircular opening 13.

The outer circumferential surface of the advancing run 1a of thetransfer conveyor 1 is surrounded by the three correction rollers 22 ofthe upper correction device A1 and the three correction rollers 22 ofthe lower correction device A2 with substantially equally spaceddistances in this manner.

On one side surface of the roller support frame 15 is provided an armplate 24 whose bottom end is fixed to the support frame 15 and the freeend is formed with a U-shaped slit 25. The U-shaped slit 25 is adaptedto be fitted with the shank of a bolt 28 adapted to be threadedlyengaged in the threaded aperture 27 formed in a movable member 26. Thearm plate 24 is clamped to the movable member 26 by means of the head28b of the bolt 28 threadedly engaged in the movable member 26.

The horizontal plate 16 is provided with a pair of brackets 29vertically extending therefrom. An adjusting screw shaft 30 is rotatablysupported with its ends by the brackets 29 and extends in the movingdirection of the transfer belt 1. The movable member 26 has a threadedaperture 26a adapted to engage with the threaded portion 30a of theadjusting screw shaft 30 and is movable in the moving directions of thetransfer belt 1 along the horizontal plate 16 by rotating the adjustingscrew shaft 30 about its axis. In this manner, the arm plate 24, themovable member 26, the bolt 28, the adjusting screw shaft 30 and thelike form as a whole angle adjusting means 31 for adjusting the angle ofthe roller support frame 15.

It is preferable that a device (not shown) similar to the twistcorrection device A described above is provided in the lower chamber 4bof the support frame 4 for the purpose of preventing or correcting thetwist of the returning run 1b of the transfer belt 1. However, such acorrection device for the returning run 1b may be omitted.

The operation and the adjusting method of the first embodiment will beexplained hereinafter.

When the advancing run la does not undergo any twisting, the rollersupport frames 15 of the upper and lower correction devices A1 and A2are fixed to the support frame 4 so that the vertical plate 14 isperpendicular to the advancing direction of the advancing belt 1a.

In such a case, the correction rollers 22 are positioned to cause theirshafts 23 to extend in directions perpendicular to the advancingdirection of the advancing run 1a. The correction rollers 22 are inrolling contact with the outer circumferential surface of the advancingrun 1a to guide it so that the advancing run 1a advances straight in thesimilar manner to that of the hitherto used shape-holding rollers 6.

When any twisting or twisting tendency in the advancing run 1a occurs,after the bolts and nuts 17 and 19 and the bolts 28 have been loosened,the adjusting screw shafts 30 of the angle adjusting means 31 arerotated to move the movable members 26 along the adjusting screw shafts30. Consequently, the roller support frames 15 of the upper and lowercorrection devices A1 and A2 are rotated through the same angles inopposite directions about the bolts and nuts 17, respectively.Thereafter, the roller support frames 15 inclined to the advancingdirection of the advancing run 1a are fixed to the horizontal plates 16by fastening the bolts and nuts 17 and 19 and the bolts 28.

The inclination of the roller support frames 15 relative to the twistingdirection of the advancing run 1a is such that the ends of thecorrection rollers 22 on the side of twisting direction of the advancingrun 1a of the pipe-shaped belt 1 is positioned forwardly of the otherends of the correction rollers 22 in the advancing direction of theadvancing run 1a.

With this arrangement, six (three upper and three lower) correctionrollers 22 give the advancing run 1a a strong correction force in adirection opposite to the twisting direction of the run 1a so that thetwisting can be prevented or corrected.

It is advantageous that the pipe-shaped transfer belt 1 is embraced onthe left and right sides by the correction rollers 22 in the rollersupport frame 15 in the first embodiment above described. The reason isthat the larger the inclined angles of the roller support frames 15, thehigher is the twist prevention or correction force caused by thecorrection rollers 22 more strongly urging the outer circumferentialsurface of the transfer belt 1 in a manner that the rollers 22 contactthe surface.

FIGS. 8 to 10 illustrate the second embodiment of the invention. Likecomponents are denoted by the same reference numerals as those in thefirst embodiment and will not be described in further detail.

In the second embodiment, the respective inclined angles of the rollersupport frames 15 of the upper and lower correction devices A1 and A2are able to be adjusted by means of single angle adjusting means 32simultaneously in opposite directions and in synchronism with eachother.

In more detail, the angle adjusting means 32 includes a U-shaped bracket33 facing inwardly and fixed to one side surface of the upper chamber 4aof the support frame 4. An adjusting screw shaft 34 is formed with twocontinuous screw thread portions 34a and 34b whose threads are turned inopposite directions, respectively. The adjusting screw shaft 34 issupported with its ends by the U-shaped bracket 33 and is threadedlyengaged with a movable member 35 threadedly engaged on the normal screwthread portion 34a and with a movable member 39 threadedly engaged onthe reverse screw thread portion 34b.

The roller support frame 15 of the upper correction device A1 isprovided with a horizontal arm plate 36 horizontally extending therefromon the lower side surface somewhat near its rearward end, while theroller support frame 15 of the lower correction device A2 is providedwith a horizontal arm plate 40 horizontally extending therefrom on theupper side surface somewhat near its forward end. A bolt 38 passesthrough an elongated aperture 37 formed in the horizontal arm plate 36and extending in its longitudinal direction and is threadedly engaged ina threaded aperture formed in the upper face of the movable member 35. Abolt 42 is threadedly engaged in a threaded aperture formed in the lowerface of the movable member 39 and passes through an elongated aperture41 formed in the horizontal arm plate 40 and extending in itslongitudinal direction.

With the arrangement of the second embodiment, only the rotation of theadjusting screw shaft 34 causes both the movable members 35 and 39 tomove in opposite directions in synchronism with each other causing theupper and lower roller support frames 15 to rotate about the bolts andnuts 17 in opposite directions in synchronism with each other.Therefore, the adjusting operation can be more simplified.

FIGS. 11 and 12 illustrate the third embodiment of the invention. In thethird embodiment, the center correction roller 22 of the uppercorrection device Al is able to be adjustable vertically or in radialdirections of the pipe-shaped transfer belt in a simple manner. For thispurpose, bolts 43 for mounting the support bearing 20 supporting thecenter correction roller 22 passes through vertically elongatedapertures 44 formed in a vertical plate 14. Further, the support bearing20 is provided at its upper portion with a horizontal upper plate 20a.The lower end of a female screw member 45 is fixed to the center of thehorizontal upper plate 20a.

An adjusting bolt 46 as a rotating shaft for the roller support frame 15is provided at the center of the upper horizontal plate 16 of thesupport frame 4 so as to pass through the center of the upper horizontalplate 16. Moreover, the bolt 46 is threadedly engaged in the femalescrew member 45. With this arrangement, after loosening the bolt 43, theadjusting bolt 46 is rotated to raise or lower the support bearing 20for the center correction roller 22. Therefore, the position of thecenter correction roller 22 can be adjusted simply. After the positionof the center correction roller 22 has been adjusted, the adjusting bolt46 is fixed to the support frame 4 by means of a lock nut 47 which alsoserves to fix the roller support frame 15 to the support frame 4.

The support bearings 20 on both sides other than the support bearing 20for the center correction roller 22 are mounted on the rear surface ofthe vertical plate 14 to prevent the center correction roller 22 and thesupport bearing 20 therefor from interfering with the correction rollers22 on both sides and support bearings 20 therefor.

With the construction of the third embodiment, the position of thecenter correction roller 22 can be simply adjusted in verticaldirections, while with its adjustment the three correction rollers 22can be brought into uniform contact with the outer circumferentialsurface of the advancing run 1a of the transfer belt 1 under pressure.

FIG. 13 illustrates the fourth embodiment of the invention. The twistcorrection device A' in the fourth embodiment is similar in constructionto that obtained by rotating the correction device in the firstembodiment through 90 degrees in a vertical plane. In other words, thetwist correction device A' includes the right correction device A1'viewed in FIG. 13 obtained by rotating the upper correction device A1 inthe first embodiment shown in FIG. 5 through 90 degrees in the clockwisedirection in the drawing, and the left correction device A2' obtained byrotating the lower correction device A2 through 90 degrees in theclockwise direction in the drawing. The advancing run la of a transferbelt 1 is surrounded by the six (3×2) correction rollers 20 supported bythe roller support frames 15 of the right and left correction devicesA1' and A2'.

Other components of constitution and operation of the fourth embodimentare substantially similar to those in the first embodiment. Moreover,the fourth embodiment can bring about the same effect as that of thefirst embodiment.

FIG. 14 illustrates the fifth embodiment of the invention. In the fifthembodiment, the adjusting screw shaft 34 in the second embodiment shownin FIG. 10 is connected to the rotary shaft 48a of a reversible motor 48(driving means) fixed to the inner surface of the support frame 4. Withthis arrangement, the adjusting screw shaft 34 is rotated through adesired number of rotations in a desired direction. It is preferablethat the motor 48 is a step-motor which is controlled with the aid of aknown twist detecting device 70 which is able to automatically detectdirections and amount of twisting of the transfer belt 1. The otherconstitution of the fifth embodiment is substantially similar to that inthe second embodiment. However, members corresponding to the bolts andnuts 19 in the second embodiment may be saved or may be loosened if theyare provided. Moreover, members corresponding to the bolts and nuts 38and 42 are loosened.

In the fifth embodiment, the roller support frames 15 can be rotated bymeans of the motor 48 without human power. Moreover, the twistcorrection device has an advantage in that it can be automaticallycontrolled in conjunction with the known twist detecting device.

FIG. 15 illustrates the sixth embodiment of the invention. To the innersurface of the support frame 4 is fixed a known motor driven jack 49(driving means) whose support head 49a is adapted to extend and retractabove its main body 49b. Moreover, to the inner surface of the supportframe 4 is fixed the upper end of a guide rod 50 extending verticallyand immediately above the support head 49a. Four points for forming arhombic link mechanism are the support head 49 of the motor driven jack49, a slide member 51 slidably fitted on the guide rod 50, the rearwardend of an arm plate 52 extending rearward and fixed to the side surfaceof the roller support frame 15 of the upper correction device A1, and aforward end of an arm plate 53 extending forward and fixed to the sidesurface of the roller support frame 15 of the lower correction deviceA2.

These four points are connected by four link members 55 and shafts 56extending in transverse directions to form a rhombic link mechanism 54.When the support head 49a of the motor driven jack 49 is moved towardand away from the main body 49b, the rhombic link mechanism 54 iselongated or contracted in vertical directions so that the rearward endof the arm plate 52 and the forward end of the arm plate 53 are movedtoward and away from each other, with the result that the upper andlower roller support frames 15 are moved in opposite directions insynchronism with each other.

The other elements constituting the sixth embodiment are similar to thatof the fifth embodiment. Moreover, the sixth embodiment can bring aboutthe same effect as that of the fifth embodiment.

FIG. 16 illustrates the seventh embodiment of the invention. In theseventh embodiment of the invention, an arm plate 52 extending rearwardis fixed to the side surface of the roller support frame 15 of the uppercorrection device A1, while an arm plate 53 extending forward is fixedto the side surface of the roller support frame 15 of the lowercorrection device A2. To the rearward end of the arm plate 52 isconnected the head end of the cylinder 57a of a hydraulic or pneumaticcylinder unit 57 (driving means), and the rod end of the piston rod 57bof the cylinder unit 57 is connected to the forward end of the arm plate53. Hydraulic (or pneumatic) pressure supplied into the cylinder 57a iscontrolled to extend or retract the piston rod 57b from or into thecylinder 57a so that the upper and lower roller support frames 15 aremoved in opposite directions in synchronism with each other.

The hydraulic cylinder unit 57 is not supported by the support frame 4.However, the correction rollers 22 supported by the upper and lowerroller support frames 15 are automatically positioned at properpositions where reaction forces applied to the correction rollers 22from the transfer belt 1 become substantially equal. Therefore, theupper and lower roller support frames 15 do not displace in anuncontrolled state.

The other element constituting the seventh embodiment are similar tothat of the fifth embodiment. The seventh embodiment can bring about thesame effect as that of the fifth embodiment. Moreover, the seventhembodiment has an advantage in that the construction can be simplified.

FIGS. 17 and 18 illustrate the eighth embodiment of the invention. Inthe eighth embodiment, to the side surface of the roller support frame15 of the upper correction device Al is fixed a toothed member 58 formedin its lower edge with teeth 58a which are arranged in an arcuate shapein a horizontal plane having a center at the bolt and nut 17 (FIG. 4),while the side surface of the roller support frame 15 of the lowercorrection device A2 is fixed a toothed member 59 formed in its upperedge with teeth 59a which are arranged in an arcuate shape in ahorizontal plane having a center at the bolt and nut 17 (FIG. 4). Apinion 60 is fixed to the rotating shaft 61a of a reversible motor 61(driving means) fixed to the support frame 4 so that the pinion 60 is inmesh with the upper and lower teeth 58a and 59a of the upper and lowertoothed members 58 and 59. With this arrangement, when the pinion 60 isrotated in normal or reverse direction by means of the motor 61, theupper and lower roller support frames 15 are moved in oppositedirections in synchronism with each other.

The other elements constituting the eighth embodiment are similar tothat of the fifth embodiment. The eighth embodiment can bring about thesame effect as that of the fifth embodiment. Moreover, the eighthembodiment has an advantage in that the construction can be simplified.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the other changes in form and details canbe made therein without departing from the spirit and scope of theinvention. For example, the invention can be modified in the followingmanner.

(1) Correction rollers more than two or four are provided in one rollersupport frame.

(2) The angle adjusting means is rotated by means of a unit other thanthose shown. For example, shafts for pivotally supporting the rollersupport frames are rotated through reduction gears by a handwheel or amotor.

As can be seen from the above description, according to the inventiononly by adjusting the inclined angle of only one roller support frame bymeans of only one angle adjusting means, the inclined angles of aplurality of correction rollers can be simultaneously by equal values sothat adjusting operation can be rapidly and simply carried out.

What is claimed is:
 1. A twist correction device for a pipe conveyorhaving an endless transfer belt whose at least part is rounded in a pipeshape enclosing therein a material to be transferred, wherein the devicecomprises a plurality of correction rollers obliquely inclined relativeto the transfer direction of the transfer belt and in pressure contactwith the outer circumferential surface of the pipe-shaped transfer beltto apply correcting force to the belt for correcting twisting of thebelt, two roller support frames supporting the plurality of correctionrollers, respectively, and pivotally connected to a stationary supportframe rotatably about axes perpendicular to the transfer direction ofthe transfer belt, and angle adjusting means provided on the stationarysupport frame for adjusting rotated angles of the roller support framesabout the axes, thereby correcting twisting of the pipe-shaped transferbelt.
 2. The twist correction device for a pipe conveyor as set forth inclaim 1, wherein the angle adjusting means provided for each of theroller support frames comprises an arm plate fixed to one of the rollersupport frames, an adjusting screw shaft rotatably supported by thesupport frame, a movable member movable along the adjusting screw shaftby rotating it, and fastening means for loosely connecting the arm plateand the movable member, thereby adjusting the rotated angle of theroller support frame about the axis by rotating the adjusting screwshaft.
 3. The twist correction device for a pipe conveyor as set forthin claim 1, wherein the angle adjusting means comprises arm plates fixedto the roller support frames, respectively, an adjusting screw shaftrotatably supported by the support frame, movable members movable inopposite directions along the adjusting screw shaft by rotating it, andfastening means for loosely connecting the arm plates and the movablemembers, respectively, thereby simultaneously adjusting the rotatedangles of the roller support frames about the axes by rotating theadjusting screw shaft.
 4. The twist correction device for a pipeconveyor as set forth in claim 1, wherein at least one correction rolleris adjustable in radial directions of the pipeshaped transfer beltrelative to the relevant roller support frame.
 5. The twist correctiondevice for a pipe conveyor as set forth in claim 4, wherein saidradially adjustable correction roller is arranged on one side of therelevant roller support frame, while the remaining correction rollersare arranged on the other side of the roller support frame, therebypreventing any interference with the correction rollers.
 6. The twistcorrection device for a pipe conveyor as set forth in claim 1, whereinthe two roller support frames are arranged one above the other.
 7. Thetwist correction device for a pipe conveyor as set forth in claim 1,wherein the two roller support frames are arranged side by side inhorizontal.
 8. The twist correction device for a pipe conveyor as setforth in claim 1, wherein said angle adjusting means comprises drivingmeans for rotating the roller support frames about the axes by powermeans.
 9. The twist correction device for a pipe conveyor as set forthin claim 1, wherein the angle adjusting means comprises arm plates fixedto the roller support frames, respectively, an adjusting screw shaftrotatably supported by the support frame, a reversible motor whoseoutput shaft is connected to the adjusting screw shaft, movable membersmovable in opposite directions along the adjusting screw shaft byrotating it, and fastening means for loosely connecting the arm platesand the movable members, respectively, thereby simultaneously adjustingthe rotated angles of the roller support frames about the axes byrotating the adjusting screw shaft by the reversible motor.
 10. Thetwist correction device for a pipe conveyor as set forth in claim 9,wherein said reversible motor is controlled by twist detecting means forautomatically detecting directions and amounts of twisting of thetransfer belt.
 11. The twist correction device for a pipe conveyor asset forth in claim 1, wherein the angle adjusting means comprises aslide member movable guided by a guide rod fixed to the support frame,arm plates connected to the two roller support frames, respectively, andtheir free end extending in opposite directions to each other, a motordriven jack fixed to the support frame and having a support headextendable and retractable relative to the main body of the jack, andfour link members, and the slide member is pivotally connected to thefree ends of the arm plates by the two link members, while the supporthead of the motor driven jack is pivotally connected to the free ends ofthe arm plates by the remaining two link members to form a rhombic linkmechanism, thereby simultaneously adjusting the rotated angles of theroller support frames about the axes by extending and retracting thesupport head relative to the main body of the motor driven jack.
 12. Thetwist correction device for a pipe conveyor as set forth in claim 1,wherein the angle adjusting means comprises arm plates connected to thetwo roller support frames, respectively, and their free ends extendingin opposite directions to each other, and a cylinder unit whose cylinderhead end and the piston rod end are pivotally connected to the free endsof the arm plates, respectively, thereby simultaneously adjusting therotated angles of the roller support frames about the axes by extendingand retracting the piston rod relative to the main body of the cylinderunit.
 13. The twist correction device for a pipe conveyor as set forthin claim 1, wherein the angle adjusting means comprises a reversiblemotor fixed to the support frame, a pinion connected to the rotatingshaft of the reversible motor, and two toothed members each formed inone edge with teeth which are arranged in an arcuate shape in ahorizontal plane and having a center at the rotating axis of therelevant roller support frame, said two toothed members being fixed tothe two roller support frames, respectively, such that the teeth of thetwo toothed members are in opposition to each other and simultaneouslyin mesh with the pinion connected to the rotating shaft of thereversible motor, thereby simultaneously adjusting the rotated angles ofthe roller support frames about the axes by energizing the reversiblemotor.